1. Field of the Invention
The present invention relates to an ink jet recording apparatus using an ink jet printing head to perform printing a paper web with jets of ink and, in particular, an ink jet printing head of drop-on-demand type having a nozzle assembly which comprises a plurality of nozzle rows juxtaposed with one another in a direction of travel of the paper web to give the nozzle assembly a predetermined length in the direction of travel of the paper web, each of the nozzle rows having a multitude of ink nozzles juxtaposed with one another in a direction of width of the paper web.
2. Description of the Prior Art
In an ink jet recording apparatus, it is an important requisite in providing good printing quality that the spacing between an ink jet printing head and the surface of a paper web (printing surface) be held constant. When use is made of an ink jet printing head which as in an ink jet recording apparatus as described, e. g., in U.S. Pat. No. 6,003,988, has a nozzle assembly made of only a single nozzle row having ink nozzles juxtaposed with one another in a direction perpendicular to a direction of travel of the paper web, namely in a direction of width of the paper web, the curving of a paper web traveling path with the paper web wrapped on a roller surface does not hinder printing on the paper web. However, when use is made of an ink jet printing head of drop-on-demand type which as in an ink jet recording apparatus as described, e. g., in JP H11-034360 A, has a nozzle assembly made of a plurality of nozzle rows juxtaposed with one another in a direction of travel of a paper web, the ink discharge ports in these nozzle rows arranged in the direction of travel of paper must have their front ends arranged in a plane whereby if the paper web traveling path is curved with the paper web wrapped on a roller surface, a change may be created in distance between the front ends of the ink nozzles (ink discharge ports) and the paper surface along the direction of travel of the paper web. If this occurs, printing problems such as a printed image being out of register and a distorted print image are significantly brought about. Thus, a nozzle head with a nozzle assembly having a predetermined length in a direction of travel of a paper web gives rise to such printing problems.
There is also known as disclosed in JP H05-124284 A an ink jet recording apparatus in which a plate-like guide member is disposed below a paper web traveling path between a plurality of rollers so that a paper web is urged against the guide member and a single ink jet printing head is disposed opposite and parallel to the surface of the paper web. Further, as disclosed in JP 2000-141618 an ink jet recording apparatus is known in which a plurality of ink jet printing heads are arranged each opposite and parallel to a surface of paper web between rollers on which the paper web is wrapped while having a tension applied to it.
In an apparatus of this type having a single ink jet printing head or a plurality of ink jet printing heads which is or are each disposed parallel to the paper surface between the guide rollers, the or each ink jet printing head may be an ink jet heat of drop-on-demand type and with a nozzle assembly having a plurality of nozzle rows juxtaposed with one another in a direction of travel of the paper web to be able generally to perform printing without adverse influence from a paper wrap angle for a guide roller because it is placed opposite and parallel to the paper surface between the rollers. However, in the ink jet recording apparatus of this type, if the rollers guiding paper while wrapping it on them are spaced from each other by a long distance, it is no longer possible to completely eliminate fluttering of the paper web traveling between the guide rollers. Fluttering of the paper web may occur between the rollers while it is driven to travel at a high speed or when the speed changes. Then, the result may be a disorder created in a printed image or a failure to print with due accuracy.